It's based in European, and more specifically, British Enlightenment thinking, the apotheosis of which (with regard to freedom of speech) is On Liberty[0] by John Stuart Mill, an Englishman. To quote:
> THE TIME, it is to be hoped, is gone by, when any defence would be necessary of the "liberty of the press" as one of the securities against corrupt or tyrannical government. No argument, we may suppose, can now be needed, against permitting a legislature or an executive, not identified in interest with the people, to prescribe opinions to them, and determine what doctrines or what arguments they shall be allowed to hear. This aspect of the question, besides, has been so often and so triumphantly enforced by preceding writers, that it needs not be specially insisted on in this place.
It appears his hopes would bring disappointment were he still around.
[0] Chapter II: Of the Liberty of Thought and Discussion https://www.bartleby.com/130/2.html
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Edit: Fixing markup. If anyone knows of a document describing the markup rules, please let me know, it would save me an awful lot of edits ;-)
I'm sorry but you don't. (Also, don't I get to decide that, not you?)
> Freedom of conscience seems pretty uncontroversial, and it's what Paine is talking about in the quote you gave (on my interpretation).
Paine and Mill weren't just talking about freedom of conscience or thought. Paine thought it crucial to hear others' ideas so that he could avoid being wrong. That requires the ideas be expressed. Likewise with Mill. Chapter 2 of On Liberty is titled "Of the Liberty of Thought and Discussion"[1]. Throughout the text, Mill defends expression as well as thought, and condemns the silencing of any expression of opinion:
> But I deny the right of the people to exercise such coercion, either by themselves or by their government. The power itself is illegitimate. The best government has no more title to it than the worst. It is as noxious, or more noxious, when exerted in accordance with public opinion, than when in opposition to it.